The subject matter disclosed herein generally relates to rotors for aircraft use. More specifically, the subject disclosure relates to flexbeam rotors for helicopters or other rotorcraft.
In typical flexbeam helicopter rotors, a flexbeam extends from a rotor hub and is connected to a torque tube and blade via a bolted joint at, for example, midspan of the rotor. The joint comprises a pattern of two or more fasteners, in some rotors four or six fasteners, such as bolts, extending through the torque tube, rotor blade and flex beam at that location, in a direction perpendicular to the torque tube and rotor blade. The joint is utilized to restrict relative motion of the torque tube, rotor blade and flex beam, and to provide a load path for loads acting on the rotor blade to be transmitted to the flex beam and then into the rotor hub.
To accommodate the array of bolts at the joint, a height of the blade assembly must be increased at the joint location, which results in increased drag for the rotor blade assembly. Further, heads of the bolts and/or nuts used in the joint are often left protruding from the outer mold line, or outer design surface of the rotor blade, resulting in yet additional drag on the rotor blade. Further, a hole pattern for the bolted assembly is difficult to fabricate, as very close tolerances on hole sizes and positions must be maintained to ensure that the bolts can be installed through the three components, while still fitting the bolts closely enough to restrict relative motion and provide the load path as intended. Additionally, the joint comprising a pattern of multiple bolts requires a high preload, in some assemblies in the range of 15,000 pounds force, which may damage composite parts used in the assembly, or alternatively requires a very robust design of the components resulting in increased weight of the components and the rotor blade assembly.